Wood and stem anatomy of Rhabdodendraceae is consistent with placement in Caryophyllales sensu lato

Abstract

Qualitative and quantitative data are given for two species of Rhabdodendron. Newly reported for wood of the family are vestured pits in vessels and tracheids, nonbordered perforation plates, abaxial axial parenchyma, and presence of sphaerocrystals. Although treated variously in phylogenetic schemes, Rhabdodendron is placed in an expanded Caryophyllales in recent cladograms based on molecular data. This placement is consistent with features characteristic of most families of the order, such as nonbordered perforation plates and successive cambia. Primitive character states in Rhabdodendron (tracheids, diffuse axial parenchyma, ray type) are shared with Caryophyllales s.l. that branch near the base of the clade: Agdestis, Barbeuia, Simmondsia, and Stegnosperma. Presence of vestured pits in vessels and silica bodies in wood, features not reported elsewhere in Caryophyllales s.l., are shared by Rhabdodendron and Polygonaceae. Wood of Rhabdodendron has no features not found in other Caryophyllales, and is especially similar to genera regarded as closely related to it in recent phylogenetic hypotheses. Successive cambia that are presumably primitive in the clade that includes Rhabdodendron are discussed. Distinctions between sphaerocrystals and druses are offered.